Thanks for the info guys you all made me think twice about getting a R154 lol, i dont think its worth it now, i would be better off with a R150 or R150F instead, so all i need to bolt to any R series trans is a bellhousing from a R151F truck right, kool. I think will look into the R150 or R150F 
ok R150 and R150F both have chain drive tcases, what you want is gear driven cases, so stick with either a W56 or a R151, both bolt to gear driven tcases
UNLESS you need a driverside drop tcase then the R150 f is what you need
